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Title: Simulation of surface acoustic wave modulation of quantum cascade lasers
Author: Cooper, Jonathan David
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2013
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Frequency tunable quantum cascade lasers (QCLs) with a broad wavelength tuning range are highly desirable in chemical sensor/spectroscopic applications owing to the wide range of frequencies, from terahertz up to mid-infrared, which must be scanned. QCLs represent the only convenient, low-cost radiation source over this range of frequencies, however little progress has been made in achieving broadband tunability. Surface acoustic waves (SAWs) present an opportunity for achieving broadband modulation by passing a SAW through the gain medium of the QCL. The electric �eld generated by the SAW via the piezoelectric e�ect will modulate the carrier concentration within the gain medium causing distributed feedback (DFB) in the QCL. Unlike conventional DFB mechanisms such as etched gratings on the QCL surface, the wavelength of the SAW, and therefore the pitch of the DFB, can be altered allowing tunability in the QCL frequency. In this work, a theoretical investigation into the interaction between a SAW and the free-carriers within the QCL active region is presented, with particular focus on whether this interaction is strong enough for DFB to occur. Numerical models of both QCL active regions and SAW propagation through semiconductor materials are developed and used in conjunction to simulate the modulating e�ect of the SAW on the carrier concentration in the QCL. It is shown that the magnitude of this modulation is large enough for DFB occur, giving a DFB coupling constant comparable to, if not larger than, many experimentally demonstrated DFB QCLs. Finally, device design recommendations are presented which aim to maximise this DFB coupling constant in order to give the widest possible tuning range of the QCL emission frequency.
Supervisor: Cunningham, John ; Harrison, Paul ; Ikonic, Zoran Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available